Full PBX telephony feature preservation across a voice over packet network

ABSTRACT

A method for providing supplementary services in a packet voice network. The method includes the steps of receiving a list of information elements from a sending station and then inserting the list into a call control message. The message is inserted in such a manner as to ensure that any supplementary services information included in the information elements is preserved. In addition locally significant messages are included in a globally significant message so any supplementary services information in the locally significant messages is preserved. After the supplementary services information is preserved, the messages are sent to a receiving station. A network device operable to provide this functionality is also discussed.

BACKGROUND

1. Field

This disclosure relates to voice over packet networks, more particularlyto providing full PBX feature transparency across voice over packetnetworks.

2. Background

If users move from a traditional, public switched transmission network(PSTN) phone system to a packet voice phone system, they can obtainseveral advantages. Voice over packet networks typically use existingdata networks, avoiding large network change over costs. Coding andpacketizing voice signals and routing them across existing packetnetworks also saves considerable costs on long-distance charges. Usingexcess capacity on existing data networks also makes those networks moreefficient and cost effective.

Most of these advantages result from the connections to the outsideworld from a company's internal phone system. One example of an internalphone system is a PBX, or private branch exchange. Changing thetraditional PBX to a packet voice network may cause some features to belost.

In the ISDN (integrated services digital network) environment, there aretwo classes of service, basic and supplementary. The difference betweenthe two classes lies in their ability to stand alone. Stand-aloneservices are basic services. Supplementary services rely upon thepresence of another service to operate. Examples of supplementaryservices include call waiting, call hold, completion of call to busysubscriber, call transfer, call forwarding, etc. These will also bereferred to as PBX features, since they are typically associated withPBX service. A packet voice network should maintain these features toprovide users with no loss of features.

When packet networks replace PBXs, however, a problem can arise withcertain types of control messages. Network devices in the packet networkmay drop control messages occurring between two directly connectednodes, referred to as local messages. Since the messages are onlylocally significant, the routers do not send them to other stations onthe network. A problem arises when two nodes are connected through athird node. The middle node drops the locally significant messages,which may affect the network's ability to provide supplementaryservices. Some supplementary services depend upon the local messages tooperate.

For example, when one end node disconnects from the network such as whenthe user hangs up, that node sends a disconnect message on the data (D)channel to the middle node. The middle node responds with a RELEASEmessage to the end node before passing the disconnect to the other endnode. A RELEASE message releases the B channel used by the end node toconnect with the middle node and ultimately the other end node. Thissequence effectively prevents any supplementary services from beingpassed from the one end node to the other. Because the middle node doesnot pass on the RELEASE message, since it is of local significance, anysupplementary services information in that message does not pass either.This is also true of any supplementary service elements being carried bythe RELEASE COMPLETE messages.

Therefore, a method to provide supplementary services informationcontained in locally significant messages to non-local nodes on thepacket voice network is needed. This would allow users to continue tohave all the features available on traditional PBXs, with all theadvantages of a packet voice network.

SUMMARY

One aspect of the invention is a method for providing supplementaryservices in a packet voice network. The method includes the steps ofreceiving a list of information elements from a sending station and theninserting the list into a call control message. The message is insertedin such a manner as to ensure that any supplementary servicesinformation included in the information elements is preserved. Inaddition locally significant messages are included in a globallysignificant message so any supplementary services information in thelocally significant messages is preserved. After the supplementaryservices information is preserved, the messages are sent to a receivingstation. Typically, the message from within which the informationelements are received will be a Q.931 message.

Another aspect of the invention is a network device operable to includesupplementary services information normally transmitted in a PBX invoice over packet network transmissions. One embodiment of the networkdevice has two communication devices, with a transit node between them.The messages are transferred through the transit node such that thelocally significant messages are preserved, as well as Q.931 informationelements translated into call control messages for a packet voicenetwork.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be best understood by reading the disclosure withreference to the drawings, wherein:

FIG. 1 shows a prior art network block diagram and call disconnectionsequence.

FIG. 2 shows one embodiment of a network block diagram and calldisconnection sequence in accordance with the invention.

FIG. 3 shows one embodiment of a network device allowing transfer ofsupplementary services, in accordance with the invention.

FIG. 4 shows a flowchart of one embodiment of preserving supplementaryservices information, in accordance with the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Integrated services digital network (ISDN) provides digital telephoneservice to users. ISDN interfaces are time division multiplexed intochannels. Control and data signals are separated into differentchannels. Data, or D, channels handle control signals andbi-directional, or B, channels handle data. The data may include voicesignals, data signals and video signals. The B channels have 64,000 bitsper second (kbps) bandwidth.

Two primary variants of ISDN are basic rate interface (BRI) and primaryrate interface (PRI). BRI provides two B channels and one D channel andis often referred to as 2B+D. PRI service typically runs over a T1 or E1line. PRI over a T1 line offers 23B+D service. The D channel for PRI has64 kbps and for BRI has 16 kbps bandwidth.

A number of international standards define ISDN. The InternationalTelecommunications Union (ITU) provides most of them. I.430 describesthe Physical layer and part of the Data Link layer for BRI. Q.921documents the Data Link protocol used over the D channel. Q.931documents the Network layer user-to-network interface and is of the mostinterest here. Q.931 provides call setup and breakdown, channelallocation, and a variety of optional services. One set of theseoptional services is referred to as supplementary services.

As mentioned previously, supplementary services are those services thatdepend upon the presence of another service to be available. Basicservices are those that stand alone. Supplementary services includefeatures typically offered to users within businesses, such as callforwarding, call hold, call transfer, etc.

The tasks accomplished using the Q.931 standard, such as call setup andbreakdown, are completed on the data channel using messages formatted inaccordance with the standard. These messages are referred to as callcontrol messages. Q.931 was promulgated as an ISDN-specific standard.However, voice over packet networks use variants of Q.931 messaging.Because of this, the same message names are typically used. Therefore,for example, a DISCONNECT message in VoX networks will perform analogousto the DISCONNECT message provided in the Q.931 specification. There aresome variations, as will be discussed further.

Currently, three types of packet networks are used to transmit voicedata. Voice over Internet Protocol (VoIP) devices transmit voice data inpackets across networks using the Internet Protocol. Voice overAsynchronous Transfer Mode (VoATM) transmits voice data as cells acrossan ATM network. Finally, Voice over Frame Relay (VoFR) transmits voicedata in frames across a Frame Relay network. The terms packets, frames,and cells, as well as other groups of data, will be referred togenerally as packets. The networks will be referred to as VoX networks,where X represents ATM, IP, FR, as well as any other network that cancarry voice data in packet form.

The commonality of call control used by these different networks andISDN offers some advantages in correcting some problems that may occurin replacing a PBX with a VoX network. One such problem is shown in FIG.1, a block diagram representation of a VoX network which may cause aloss of features that were previously available through the PBX. Themessages transmitted between nodes are sequenced by time on FIG. 1, withthe initial message at the top of the figure and the final message atthe bottom.

Node A 10 is the sending node and node C 14 is the receiving node. Theyare connected through node B 12. During the course of a call, the userat node A hangs up the phone. Node A responds by sending DISCONNECTmessage to node B. Node B generates an immediate response RELEASE tonode A before passing the DISCONNECT message to node C. RELEASE andRELEASE COMPLETE messages are only of local significance. They are onlyconsidered significant to two nodes connected directly together.Therefore, when node B receives the DISCONNECT message to which it is torespond, node B sends the RELEASE message prior to passing theDISCONNECT to node C.

Node A and node B continue with the call releasing routine regardless ofwhat is happening between node B and node C. Node A returns a RELEASECOMPLETE message to node B, releasing the channel. Node B then continueswith the call release messages with node C. The problem arises becausethere may be supplemental services information contained in the RELEASEand RELEASE COMPLETE messages that does not get transferred from A to Cor C to A. Nodes A and C are not directly connected, so they do notreceive any information contained in locally significant messages fromeach other. The numbers of the messages shows the sequence of themessages, 1 through 12.

An example of this problem occurs using Ericsson QSIG. Q identifies anendpoint of an ISDN connection and SIG means signaling, so QSIG is asignaling protocol for ISDN endpoints. It is typically used in networksof PBXs. Ericsson QSIG relies upon user-to-user (UU) informationelements sent in RELEASE messages to be passed between the involved PBXsfor some supplementary services to work correctly. For example, callforward across a VoX fails to work on some versions because the networkdevices of the VoX do not pass the UU information elements in theRELEASE message back to the originating PBX.

One embodiment of a solution to this problem is shown in FIG. 2. Atransit node 16 replaces node B 12 of FIG. 1. In general terms, node Bfrom FIG. 1 is also a transit node, as that term typically applies toany intermediate node in a VoX network. However, transit node as usedhere will apply to a node that passes locally significant messages endto end rather than restricting them to directly connected nodes.

As will be discussed further, transit node B has a combination ofdevices rather than being just a solitary device or bridge as shown inFIG. 1. This combination of devices allows the network device of thetransit node in FIG. 2 to function more effectively in preservingsupplementary services.

Following the example used previously, the user at node A 10 hangs upthe phone during a VoX call. This generates a DISCONNECT message to thetransit node 16. The transit node 16 then performs some internalhandling and passes the DISCONNECT message to the receiving node C. NodeC generates a RELEASE message that is passed back to the transit node.The transit node again performs some internal message handling andpasses the RELEASE message back to node A. Node A responds with RELEASECOMPLETE and the transit node passes this back to node C. The messagesare again numbered by their sequence. In this manner, any supplementaryservices information is passed end to end, rather than being stopped atthe intermediate node.

An example of a network device that can function in the manner describedabove as a transit node is shown in FIG. 3. The transit node 16comprises a network device, in this example. The network device has twocommunication devices 18 and 22 and a tandem node 20. The tandem node 20is optional. In some environments and depending upon the functionalityof the communication devices, the tandem node will not be necessary. Thecommunication devices could be of several different types, includingrouters.

As can be seen by FIG. 3, the internal messaging of the transit node 16involves a mapping or insertion of information from the Q.931 messagesinto other types of Q.931 messages. The network device communicates withnode A from FIGS. 1 and 2 through communication device 18 and with nodeC through communication device 22. When the DISCONNECT message isreceived from node A, communication device 18 maps or otherwise insertsthe supplementary services information into a FACILITY message. Thetandem node 20 then passes the FACILITY message to the communicationsdevice 22. Communication device 22 then interprets the header on theFACILITY message, converts it to a DISCONNECT message and sends it tothe other end node.

It should be noted that the DISCONNECT message must be mapped to aFACILITY message in some environments, or the supplementary servicesinformation will not be transferred. For example, in H.225 compliantsystems, there is only a single call teardown message. When the initialdisconnection or teardown message is sent, it is assumed to be the lastcommunication between the two legs of the call. In this case, none ofthe subsequent messages would be transmitted and no supplementaryservices information will be sent. The mapping of the DISCONNECTmessages to the FACILITY message postpones the actual teardown of thecall legs, until the RELEASE COMPLETE message is received and endingtransfer of the supplementary services information.

The other end node returns with a RELEASE message that includessupplementary services information. The RELEASE message is then mappedor otherwise inserted into a FACILITY message, which traverses thetandem node in the opposite direction. Communication device 18 convertsit to the locally significant RELEASE message. When communication devicereceives the RELEASE COMPLETE message from the originating node, it mapsor otherwise inserts the supplementary services information and themessage into a DISCONNECT message, which traverses the tandem node.Finally, communication device 22 converts the information in theDISCONNECT message back to the locally significant RELEASE COMPLETEmessage to be communicated to the receiving node.

This network device may not be a new hardware device. Instead it may beimplemented as a software upgrade to the existing network devices.Additionally, while the block diagram shows that the communicationdevices are separate devices, this is only used for better explanationof the invention. The communication devices may actually be contained inone network device such as a router or bridge. The software upgradewould be distributed through some type of computer readable medium, suchas a downloadable file installed into the network device via a networkor loaded from a directly connected computing device. In either case, acomputing device would be responsible for reading the medium to installthe software. This software will have the functionality discussed above,the inclusion of locally significant messages in global significantmessage formats for transferring supplementary services information fromone end to the other.

The mapping or insertion of the supplementary services information mayhave two parts. One part is that discussed above, where a locallysignificant message is mapped into a globally significant message. Theother part is preservation of Q.931 supplementary services informationin general, as VoX networks use their own call control protocols thatare analogous to Q.931. As mentioned previously, Q.931 formats andfunctions have analogies in VoX networks, but some function is slightlydifferent ways. However, all VoX networks have information elements aspart of the message payload.

Therefore, one part of preserving supplementary services informationinvolves inserting or including all the Q.931 information elements sentthrough the VoX network. Rather than a complex mapping of Q.931information elements to the respective VoX call control protocol, theencapsulated list of information elements is simply appended to the tailof the equivalent VoFR or VoATM call control message. Alternatively, itcould be mapped or otherwise inserted into a USER INFORMATION element ofthe H.225 call control used in VoIP. This solution has the advantage ofpassing the information elements end to end without any interpretation.This also has the advantage of not violating VoIP H.225 standards, northose of VoFR or VoATM.

The standard Q.931 message format is shown below.

Protocol Length of Information Descriptor CR Call Reference (CR) TypeElements 1 byte 2 bytes 3 − n bytes n + 1 bytesMessages with this format are encapsulated by removing the protocoldescriptor, call reference length, call reference and message type.These fields are either of local significance or can be obtained fromthe context of the call control software in the network device.

The encapsulation format of the list of information elements isillustrated in the diagram below.

Field Protocol ID Length List of Information Elements TSP Header 4 bytes2 bytes Max of 8*260 bytes 1 byte

The field protocol ID is used to identify the Q.931 aspects of theelement encapsulated so that any interested network device can analyzeand dissect information contained in the elements while being aware ofthe context of the protocol aspects to which the elements belong. Theprotocol id most significant byte is used to indicate the version of theencapsulation format. Call control software versions on the networkdevices can correlate with the encapsulation version. The length fieldindicates the size of the list of elements in bytes. The list ofinformation elements is the actual body of the Q.931 message. The TSP(telephony service provider) header is used by the call control softwarein the network device to reflect the mapping of locally significantmessages to globally significant messages as described above.

In this manner, the two mechanisms discussed above serve to preservesupplementary services information when a phone system converts from aPBX to a VoX network. The supplementary services information arepreserved by application of the invention. One embodiment of a methodfor performing such preservation is shown in FIG. 4.

A network device, such as that shown in FIG. 3, receives the informationelements typically through a Q.931 message at 26. The informationelements from the Q.931 are then inserted into the analogous callcontrol message for the VoX network at 28. If the Q.931 message is alocally significant message, it is included by inserting or including itas a globally significant message at 30. These processes serve topreserve the supplemental services information typically availablethrough PBXs. In this manner features available prior to changing from aPBX system to a VoX system remain available to the users. These messagesare then sent at 32.

The specific examples given above indicate that only the locallysignificant messages of RELEASE and RELEASE COMPLETE are mapped into theglobally significant messages of DISCONNECT and FACILITY. However, thesewere not intended to limit application of the invention. Any locallysignificant message could be mapped to any globally significant message.In this manner, locally significant messages are passed transparentlyend to end without violating any VoX constrictions, such as H.225messages in an IP network.

Further, while this invention is envisioned to be applied to an ISDNnetwork using Q.931 call control messaging from the end nodes, it may beapplied to any network running standardized call control messages with aseparate call control channel. ISDN networks will more than likelycontinue to use Q.931 standardized messages, but application of thisinvention is not restricted to this particular call control message.

Thus, although there has been described to this point a particularembodiment for a method and apparatus for full PBX feature preservationin VoX networks, it is not intended that such specific references beconsidered as limitations upon the scope of this invention exceptin-so-far as set forth in the following claims.

1. A method for providing supplementary services in a packet voicenetwork, the method comprising: receiving a list of information elementsfrom a sending station in a private branch exchange network; insertingthe list into a call control message such that any supplementaryservices information included in the information elements is preserved,wherein supplementary services are services that rely upon the presenceof another service to operate; mapping a locally significant messageinto a globally significant message in a private branch exchange networkwherein any supplementary services information in the locallysignificant messages is preserved, wherein a locally significant messageis a message that is otherwise not transmitted to other stations on anetwork; and sending the call control message and the globallysignificant message to a receiving station in the private branchexchange network.
 2. The method of claim 1 wherein the list ofinformation elements are received as a Q.931 message.
 3. The method ofclaim 1 wherein the inserting the list further comprises appending theinformation elements to a call control message for a voice over packetnetwork.
 4. The method of claim 1 wherein the inserting the list furthercomprises mapping the information elements into the user informationelement of an H.225 message.
 5. The method of claim 1 wherein the packetvoice network further comprises one of the group comprising: Voice overFR, Voice over IP and Voice over ATM.
 6. The method of claim 1 whereinthe locally significant message further comprises a RELEASE message. 7.The method of claim 1 wherein the locally significant message furthercomprises a RELEASE COMPLETE message.
 8. The method of claim 1 whereinthe globally significant message further comprises a DISCONNECT message.9. The method of claim 1 wherein the globally significant messagefurther comprises a FACILITY message.
 10. A network device for providingsupplementary services in a packet voice network, comprising: a firstcommunication device operable to communicate with a sending node; asecond communication device operable to communicate with a receivingnode; and a tandem node operable to transfer supplementary servicesinformation from the first communication device to the secondcommunication device such that the supplementary services information istransferred to the receiving node after the sending node sends adisconnect message thereby providing private branch exchange services,wherein the supplementary services information is acquired from alocally significant message not otherwise transmitted past the firstcommunication device and mapped into a globally significant message. 11.The device of claim 10, wherein the first and second communicationdevices further comprise routers.
 12. The device of claim 10, whereinthe first and second communication devices are part of one router.
 13. Acomputer readable medium containing software code, said code including:code operable to receiving supplementary services information from asending station in a private branch exchange network, whereinsupplementary services are services that rely upon the presence ofanother service to operate; code operable to insert the supplementaryservices information into a call control message; code operable to map alocally significant message into a globally significant message, whereina locally significant message is a message that is otherwise nottransmitted to other stations on the network; and code operable to sendthe call control message and the globally significant message to areceiving station in a private branch exchange network.
 14. The computerreadable medium of claim 13, wherein the software code is a downloadablefile distributed across a network.
 15. The computer readable medium ofclaim 13, wherein the software code is a computer file transferred froma directly connected computing device.
 16. A network device operable toprovide supplementary services information, comprising: a first meansfor communicating with a sending node; a second means for communicationwith a receiving node; and means for mapping a locally significantmessage to a globally significant message from the first means to thesecond means such that private branch exchange services are transferred,wherein the locally significant message is a message not otherwisetransmitted past the first means.
 17. A network device operable toprovide supplementary services information, comprising: a firstcommunication device operable to communicate with a sending node; asecond communication device operable to communication with a receivingnode; and the first communication device is operable to mapsupplementary to services information from a locally significant messageotherwise not transmitted base the first communication device directlyto the second communication device into a globally significant messagesuch that the supplementary services information is transferred to thereceiving node after the sending node sends a disconnect message therebyproviding private branch exchange services.